The latest version of Firefox includes more than 1,000 improvements and performance enhancements that make it easier to discover and use all of the innovative features in Firefox. This release adds support for more modern Web technologies that make it easier for developers to build amazing Firefox Add-ons, Web applications and websites.

What’s New In Firefox 5.0?

Added support for CSS animations

The Do-Not-Track header preference has been moved to increase discoverability

Tuned HTTP idle connection logic for increased performance

Improved canvas, JavaScript, memory, and networking performance

Improved standards support for HTML5, XHR, MathML, SMIL, and canvas

Improved spell checking for some locales

Improved desktop environment integration for Linux users

WebGL content can no longer load cross-domain textures

Background tabs have setTimeout and setInterval clamped to 1000ms to improve performance

Fixed several stability issues

Fixed several security issues

Looks like they are not done this year, according to Firefox’s Roadmap, Firefox 6.0 and Firefox 7.0 will be released within this year as well.